Replace the character with two other

Unfortunately, there is no way to replace all : characters in one shot. But you can do it in a loop, like this:

string s = "quick:brown:fox:jumps:over:the:lazy:dog"; int i = 0; for (;;) { i = s.find(":", i); if (i == string::npos) { break; } s.replace(i, 1, "%%"); } cout << s << endl; 

This program prints

quick%%brown%%fox%%jumps%%over%%the%%lazy%%dog 

If you need to replace only the first colon, then use the body of the loop by itself, without the loop around it.